1. Field of the Invention
This invention relates to an air compressing reciprocating in-line compression-ignition internal combustion engine comprising a plurality of fuel injecting units, which are associated with respective cylinders of the engine, and a camshaft which is mounted in cylinder head transverse walls extending between adjacent cylinders and carries injection control cams for actuating said fuel injection units by means of respective rocker levers and cam follower rollers mounted on said levers, wherein said camshaft carries beside each injection control cam valve control cams for actuating the gas exchange valves associated with one of said cylinders, and cam follower levers are provided, which are pivoted at one end in the cylinder heads of respective cylinders and at the other hand act on the gas exchange valves, possibly through intermediate elements, and have cylindrically curved surfaces engaging the calve control cams.
2. Description of the Prior Art
An engine provided with such cam mechanism is already known from Gnadt "Einspritzung bei Otto- und Dieselmotoren", Bartsch-Verlag, 1978, page 282). In that known engine the cam follower levers are pivoted on an axis which is parallel to the center line of the camshaft and each cam follower lever has a curved surface for rolling contact with the valve control cam and a nose, which is formed with a cylindrical surface and by means of an intermediate element consisting of a bucket tappet acts on the stem of the gas exchange valve. During an injection of fuel into a cylinder, the reaction force exerted by the cam follower roller of the associated rocker lever on the injection control cam acts approximately in a plane that is defined by the center line of the camshaft and the axis of the cam follower roller so that said force gives rise to bending moments tending to deform the camshaft in said plane. A disadvantage of that known cam mechanism resides in that the exertion of the fuel injection force on the injection control cam associated with a given cylinder will be accompanied by an exertion of additional forces on the injection control cams of one or both of the adjacent cylinders, in dependence on the ignition sequence. These additional forces will be due to the acceleration of the valve actuating linkage and owing to the location of the center of curvature of the engaging surface of the cam follower levers will act almost in the same plane as the fuel injection force so that they will increase the deflection of the camshaft. It must be borne in mind that the force which is due to the acceleration of the valve and exerted on each valve control cam reacts through the center of curvature of the engaging surface of the cam follower lever and the instantaneous point of contact between the engaging surface and the valve control cam. During the acceleration, that point of contact is moved to those surface portions of the cam which adjoin the base circle of the camshaft. Because the deflection of the camshaft causes the generatrices of each valve control cam to be inclined, the contacting surfaces of the valve control cam and of the cam follower ever may be overstressed so that the wear of said elements will increase and they will soon be destroyed. The known cam mechanism has been disclosed for use with cylinders provided with precombustion chambers, into which the fuel is injected only under moderate pressure resulting only in a relatively small deflection of the camshaft. The disadvantage which has been explained hereinbefore will be encountered particularly in diesel engines which are designed for a direct injection of fuel and comprise fuel injection units for generating very high fuel injection pressures in order to effect the desired atomization of fuel for an optimum combustion. But those high pressures will result in strong reaction forces on the injection control cams so that the deflection of the camshaft will be excessive. Whereas the camshafts might be so large that they will resist such strong forces, this would involve a larger expenditure of material and an increase of various dimensions adjacent to the cylinder head.
Published German Application 3,210,165 describes a valve actuating mechanism in which a cam follower lever can be tilted out of the plane in which it is actuated. In that mechanism the cam follower lever is provided adjacent to the valve with a ball head pin, which is seated in a ball socket formed in an intermediate member that is transversely displaceable on the valve stem. In that arrangement, frictional forces are effective at the interface between the intermediate member and the valve stem and in the ball socket and that interface is relatively small so that the movement of the valve may result in a tilting of the intermediate member and inaccuracies may thus be introduced into the valve control. Besides, the center of gravity of the cam follower lever and its surface engaging the valve control cam are spaced a large distance from the axis of the tilting movement, which axis extends through the centers of the ball sockets. As a result, the cam follower levers may not be sufficiently tilted for an adaptation to the plane of deflection of the camshaft when the latter rotates at high speed.